The present invention relates to a novel ion generating apparatus.
Ion beams have been created in many ways in the prior art. Ion species that are gaseous may be formed by creating a plasma from the gaseous source and extracting ions therefrom to create an ion beam. However, when the desired ion species is metallic, the problem exists in producing a plasma from the metal. In the past, hot metal vapor has been produced by elevating the metallic source to a very high temperature. For example, U.S. Pat. No. 2,882,409 describes a plasma formation by heating a metallic filament. In addition, there are certain cases where metallic gases exist at or near room temperature, but these situations are rare.
Two types of ion sources typically employed in accelerators are the: Phillips Ion Gage Ion Source (PIG) and the Duoplasmatron Ion Source.
The Duoplasmatron source forms a hot cathode arc with an intermediate electrode to constrict the discharge and to create an inhomogeneous magnetic field that concentrates the plasma near the extraction aperture in the anode. For example, U.S. Pat. No. 3,409,529 describes this type of ion source. Although the Duoplasmatron Source produces a very high ion current, it is suited for production of gaseous ions rather than metallic ions.
The PIG source utilizes two cathodes placed at the end of a cylindrical hollow anode. A magnetic field is established parallel to the anode's axis. The cathodes are at the same negative potential with respect to the anode. Electrons created by ionization of gas atoms are accelerated toward the anode but are constrained to follow the magnetic field and are thereby prevented from moving radially to the anode. Electrons oscillate between the cathodes and continue to ionize the background gas creating enough electrons to continue the ionization process. The anode typically contains a slit and an extraction electrode external to the anode. Positive ion bombardment sputters material from the cathode to form a plasma from which ions are extracted near the anode slit. Sputtering of metallic ions may be enhanced by the addition of a separate sputtering electrode. The PIG source can be used for the creation of beams of metallic ions. However, the ion beam currents achieved using the PIG souce are relatively small. U.S. Pat. No. 3,566,185 describes an ion source of this type.
U.S. Pat. No. 3,389,289 describes a plasma gun which employs powdered titanium hydride which is placed between electrodes to form a spark gap. Energizing of the electrodes produced a plasma burst.
U.S. Pat. No. 4,320,351 shows the production of an arc plasma which is sprayed onto a silicon body or wafer. The plasma is produced by injecting a powder into an arc gas stream which melts or softens the powder and propels it toward the article to be sprayed.
An article by Gilmore and Lockwood entitled Pulsed Metallic Plasma Generator published in the Proceedings of the I.E.E.E., Volume 60, #8 of August 1972 describes the production of a plasma by a vacuum arc. This method describes the placement of two electrodes in a vacuum and the establishment of an electrical discharge between them. Material from the negative electrode is vaporized and ionized by the arc to produce a metallic plasma.
U.S. Pat. No. 4,407,712 describes a sputtering technique used to plate a hollow cathode.
None of the prior art alone or in combination has described an ion beam generator for the efficient production of high current beams of metallic ions. Such a device would be a great advance in the field of production of ion beams.